| Popis: |
The underlying dynamics controlling this planet’s jet streams are complex, but it is expected that they will have an observable response to changes in the larger climatic system. A growing divergence in regional surface warming trends across the planet, which has been both observed and projected since the start of the 20th century, has likely altered the thermodynamic relationships responsible for jet stream formation and control. Despite this, the exact movements and trends in the changes to the jet streams generally remain unclear and without consensus in the literature. The latest IPCC report highlighted that trends both within and between a variety of observational and modelling studies were inconsistent (Gulev et al., 2021; Lee et al., 2021). Trends in the jet streams were associated with low to medium confidence, especially in the Northern Hemisphere. However, what is often overlooked in evaluating these trends is the confused message in the literature around how to first identify, and then characterise, the jet streams themselves. For characterisation, approaches have included isolating the latitude of the maximum wind speed, using sinuosity metrics to distinguish jet ‘waviness’, and using algorithms to identify jet cores or jet centres. Each of these highlights or reduces certain aspects of jet streams, exist within given time windows, and characterise the jet within a given (Eulerian or Lagrangian) context. While each approach can capture particular characteristics and changes, they are subject to the spatial and temporal specifications of their definition. There is therefore value in using them in combination, to assess parametric and structural uncertainty, and to carry out sensitivity analysis. Here, we describe jsmetrics v0.1.1, a new open-source Python 3 module with standardised versions of 16 metrics that have been used for jet stream characterisation. We demonstrate the application of this library with two case studies derived from ERA-5 climate reanalysis data. |
